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United States Patent |
6,240,772
|
Thomas
|
June 5, 2001
|
System and method for detecting engine malfunction based on crankcase
pressure
Abstract
A system and method for detecting engine malfunctions based on crankcase
pressure include determining a reference value indicative of current
engine operating conditions and using the reference value to determine a
crankcase pressure limit which varies as a function of the reference
value. The sensed crankcase pressure is compared to the limit to determine
when a fault condition exists. The reference value is preferably a
function of engine speed and requested engine torque and includes a second
order term multiplied by a calibratable constant which controls
sensitivity of the fault determination. The sensitivity may be adjusted to
provide equally detectable faults across all engine speeds and loads, to
be more sensitive to faults occurring at higher engine speeds, or to be
more sensitive to faults occurring at higher engine loads. The system and
method control the engine based on the determination of an engine fault.
Subsequent control may include alerting the vehicle operator, reducing
available engine torque, stopping the engine and/or logging a fault for
subsequent service or maintenance. Early cylinder/piston fault detection
provides more time for the vehicle operator and/or the engine controller
to take remedial actions to prevent more serious engine damage.
Inventors:
|
Thomas; Eric D. (Canton, MI)
|
Assignee:
|
Detroit Diesel Corporation (Detroit, MI)
|
Appl. No.:
|
207931 |
Filed:
|
December 9, 1998 |
Current U.S. Class: |
73/117.3 |
Intern'l Class: |
G01L 003/26; G01L 005/13; G01M 015/00 |
Field of Search: |
73/117.3,116
123/478
|
References Cited
U.S. Patent Documents
4223654 | Sep., 1980 | Wessel et al.
| |
4424709 | Jan., 1984 | Meier, Jr. et al. | 73/117.
|
5131371 | Jul., 1992 | Wahl et al.
| |
5165373 | Nov., 1992 | Cheng.
| |
5165579 | Nov., 1992 | Lund.
| |
5231962 | Aug., 1993 | Osuka et al.
| |
5284118 | Feb., 1994 | Kato et al. | 123/478.
|
5313924 | May., 1994 | Regueiro.
| |
5357926 | Oct., 1994 | Hu.
| |
5402760 | Apr., 1995 | Takeuchi et al.
| |
5426587 | Jun., 1995 | Imai et al. | 73/117.
|
5445128 | Aug., 1995 | Letang et al.
| |
5477827 | Dec., 1995 | Weisman, II et al.
| |
5483927 | Jan., 1996 | Letang et al.
| |
5494219 | Feb., 1996 | Maley et al.
| |
5561600 | Oct., 1996 | McCombie | 73/117.
|
5647317 | Jul., 1997 | Weisman, II et al.
| |
5687694 | Nov., 1997 | Kanno | 73/119.
|
5732676 | Mar., 1998 | Weisman et al.
| |
5771865 | Jun., 1998 | Ishida.
| |
Other References
U.S. Application No. 08/870,781, Thomas, filed Jul. 20, 1999.
|
Primary Examiner: Fuller; Benjamin R.
Assistant Examiner: Stevens; Maurice
Attorney, Agent or Firm: Brooks & Kushman PC
Claims
What is claimed is:
1. A method for detecting an engine malfunction in an internal combustion
engine, the method comprising:
sensing crankcase pressure;
determining current engine operating conditions;
determining an index value having an adjustable sensitivity based on the
current engine operating conditions;
determining a crankcase pressure limit using the index value;
comparing the crankcase pressure to the crankcase pressure limit; and
providing an engine malfunction indication when the crankcase pressure
exceeds the limit.
2. The method of claim 1 wherein determining current engine operating
conditions comprises determining a current value for engine speed.
3. The method of claim 1 wherein determining current engine operating
conditions comprises determining a current value for engine torque.
4. The method of claim 3 wherein determining current value for engine
torque comprises determining a current value for requested engine torque.
5. The method of claim 1 wherein determining an index value comprises
determining an index value with an increased sensitivity to engine speed.
6. The method of claim 1 wherein determining an index value comprises
determining an index value with a greater sensitivity to engine torque.
7. The method of claim 1 wherein determining an index value comprises
determining an index value as a function of engine speed and requested
engine torque.
8. The method of claim 1 wherein determining an index value comprises
determining an index value according to:
Index=(TQ*N.sub.e +K.sub.1 *N.sub.e.sup.2)/(K.sub.1 *K.sub.2 +1)
where TQ represents an engine torque, N.sub.e represents engine rotational
speed, K.sub.1 represents an adjustable sensitivity constant and K.sub.2
represents a scaling constant.
9. A system for detecting an engine malfunction in an internal combustion
engine, the system comprising:
a first sensor for providing a continuously variable signal indicative of
crankcase pressure;
a second sensor for determining current engine operating conditions;
a microprocessor in communication with the first and second sensors for
determining a current crankcase pressure limit based on an index value
having an adjustable sensitivity to engine operating conditions, comparing
the limit to a current crankcase pressure as indicated by the first
sensor, and controlling the engine based on a result of the step of
comparing.
10. The system of claim 9 wherein the microprocessor controls the engine by
reducing available engine torque when the current crankcase pressure
exceeds the limit.
11. The system of claim 9 wherein the microprocessor controls the engine by
stopping the engine when the current crankcase pressure exceeds the limit.
12. The system of claim 9 further comprising:
a computer readable storage medium in communication with the microprocessor
and having data stored therein representing crankcase pressure limits
accessed using the index value.
13. The system of claim 9 further comprising:
a computer readable storage medium having data representing crankcase
pressure limits accessed using the index value which varies in response to
engine speed and requested engine torque.
14. A computer readable storage medium having information stored thereon
representing instructions executable by an engine controller in
communication with a pressure transducer for detecting crankcase pressure
and a sensor for detecting engine operating conditions to determine an
engine malfunction based on the crankcase pressure, the computer readable
storage medium comprising:
instructions for sensing crankcase pressure;
instructions for determining current engine operating conditions;
instructions for determining an index value having an adjustable
sensitivity based on the current engine operating conditions;
instructions for determining a crankcase pressure limit using the index
value;
instructions for comparing crankcase pressure to the crankcase pressure
limit; and
instructions for providing an engine malfunction indication when the
crankcase pressure exceeds the crankcase pressure limit.
15. The computer readable storage medium of claim 14 wherein the
instructions for determining current engine operating conditions include
instructions for determining engine speed.
16. The computer readable storage medium of claim 14 wherein the
instructions for determining current engine operating conditions include
instructions for determining requested engine torque.
17. The computer readable storage medium of claim 14 wherein the
instructions for comparing crankcase pressure include instructions for
accessing a stored crankcase pressure limit based on the index value.
18. The computer readable storage medium of claim 14 wherein the
instructions for determining an index value include instructions for
determining an index value which is a function of fraction of engine
torque and engine speed, including a second order term to adjust
sensitivity to crankcase pressure variation in determining a crankcase
pressure fault.
19. The computer readable storage medium of claim 14 wherein the
instructions for providing an engine malfunction indication include
instructions for reducing available engine torque.
Description
TECHNICAL FIELD
The present invention relates to a system and method for detecting an
engine malfunction in an internal combustion engine using crankcase
pressure.
BACKGROUND ART
In the control of internal combustion engines, the conventional practice
utilizes electronic control units having volatile and non-volatile memory,
input and output driver circuitry, and a processor capable of executing a
stored instruction set, to control the various functions of the engine and
its associated systems. A particular electronic control unit communicates
with numerous sensors, actuators, and other electronic control units
necessary to control various functions, which may include various aspects
of engine malfunction diagnostics, fuel delivery, transmission control, or
many others.
Malfunction diagnosis in internal combustion engines is commonplace. This
is due to the desire to detect engine failures or malfunctions before they
occur, or as soon as possible after they occur, to provide an opportunity
for remedial measures to avert severe engine damage. Crankcase pressure
has been used to detect various piston-related engine malfunctions. One
method is to use a pressure limit switch which provides a signal when
crankcase pressure exceeds a predetermined threshold. This approach
requires a pressure limit switch selected based on a particular
application or an engine family which exhibits similar crankcase pressures
during operation. A crankcase pressure exceeding the predetermined
threshold results in the limit switch generating a signal which is used by
the electronic control unit to indicate a fault. The electronic control
unit may then take appropriate action depending upon the particular
application, which may include generating a warning message or indicator
light, or shutting down the engine, for example.
Another method of detecting an engine malfunction based on crankcase
pressure uses a pressure sensor which provides a continuously variable
signal representing current crankcase pressure. The electronic control
unit periodically samples the signal generated by the pressure sensor and
compares it to a predetermined crankcase pressure limit. The pressure
limit is generally a value which is determined based on expected crankcase
pressure at the maximum rated engine speed and load (or power). This
method allows the use of a single crankcase pressure sensor for a variety
of applications since the limit value may be calibrated for each engine or
engine family and stored in the electronic control unit. While this
strategy is capable of detecting various piston or cylinder-related
malfunctions at maximum speed and load, it is insufficient to detect
impending failures at lower speeds and loads. In addition, it is desirable
to detect failures or impending failures as quickly as possible to provide
the electronic control unit or the vehicle operator sufficient time to
take remedial actions to avoid a catastrophic failure.
DISCLOSURE OF INVENTION
It is therefore an object of the present invention to provide a method and
system for enhanced engine malfunction detection based on engine crankcase
pressure.
Another object of the present invention is to provide a system and method
for detecting an engine malfunction having a selectable or tunable
sensitivity for various applications.
A further object of the present invention is to provide a system and method
for detecting piston/cylinder related engine malfunctions at low engine
speeds and loads.
Another object of the present invention is to provide a system and method
for detecting an engine fault having equal detectability of excessive
crankcase pressure at all speeds and loads.
A still further object of the present invention is to provide a system and
method for engine protection which function while the engine is operating
at less than maximum power.
Yet another object of the present invention is to provide a system and
method for engine protection capable of detecting a failed piston
condition immediately after the engine is started.
In carrying out the above object and other objects and features of the
present invention, a method for detecting engine malfunctions is provided.
The method includes sensing crankcase pressure, determining a current
value for at least one engine operating parameter and comparing the
crankcase pressure to a limit which varies as a function of the at least
one engine operating parameter. The method further comprises providing an
indication that crankcase pressure has exceeded the crankcase pressure
limit and may also include controlling the engine based on the indication.
In one embodiment, an indexing value is determined based on the engine
operating parameter(s) and used to access a look-up table containing
crankcase pressure limit values. Preferably, the index value is a function
of engine speed and requested torque. Of course, the at least one engine
operating parameter may be any one or more of a variety of engine
operating parameters which are measured, sensed, calculated, or inferred,
including engine speed, actual or requested torque, oil temperature, oil
pressure, fuel temperature, coolant temperature, and the like.
In further carrying out the above objects, and other objects, features, and
advantages of the invention, a computer readable storage medium is
provided. The computer readable storage medium has information stored
thereon representing instructions executable by a computer to enhance
engine malfunction detection. The computer readable storage medium
includes instructions for determining a crankcase pressure limit based on
at least one engine operating parameter. The computer readable storage
medium also includes instructions for comparing a sensed crankcase
pressure to the determined limit and generating a signal when the sensed
crankcase pressure exceeds the limit.
A system for providing enhanced fault detection based on engine crankcase
pressure includes a crankcase pressure sensor for providing a continuously
variable signal indicative of crankcase pressure in communication with an
electronic control unit for controlling an internal combustion engine. The
system also includes at least one additional sensor which provides a
signal indicative of an engine operating parameter. The electronic control
unit includes control logic for determining a value indicative of
crankcase pressure based on a signal provided by the crankcase pressure
sensor. The electronic control unit also includes control logic for
determining a reference value indicative of engine operating conditions
based on signals provided by the at least one additional sensor. The
electronic control unit uses the reference value to determine a current
limit for the crankcase pressure and compares the crankcase pressure value
to the limit. If the crankcase pressure value exceeds the limit value, the
control logic generates a corresponding fault signal or code. The fault
code may be logged for future reference by service personnel and used by
the electronic control unit for subsequent processing which may include
illumination of a service indicator, reduction of available engine power,
and/or shutdown of the engine.
The advantages accruing to the present invention are numerous. For example,
the present invention facilitates detection of faults while the engine is
operating at less than maximum power. The present invention will redetect
a failed piston condition almost immediately after the engine is
restarted. The present invention provides a tunable fault detection
strategy which can be adjusted or calibrated to change its sensitivity
based on the particular application.
The above object and other objects, features, and advantages of the present
invention are readily apparent from the following detailed description of
the best mode for carrying out the invention when taken in connection with
the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic diagram of one embodiment for an engine malfunction
detection system based on crankcase pressure according to the present
invention;
FIG. 2 is a graph depicting normal operating crankcase pressure as a
function of an engine operating parameter along with an associated
crankcase pressure fault limit having sensitivity adjusted for a smaller
tolerance at higher engine speeds;
FIG. 3 is a graph depicting normal operating crankcase pressure as a
function of an engine operating parameter including a crankcase pressure
limit where malfunction detection is more sensitive at higher throttle
pedal position or engine load;
FIG. 4 is a graph depicting normal operating crankcase pressure as a
function of an engine operating parameter including a crankcase pressure
limit where malfunction detection is substantially equally sensitive
across engine speeds and loads; and
FIG. 5 is a block diagram illustrating operation of a system or method
according to the present invention for detecting an engine malfunction
based on crankcase pressure.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to FIG. 1, a system for detecting an engine malfunction based
on crankcase pressure according to the present invention is shown. The
system, generally indicated by reference numeral 10, includes an engine 12
having a plurality of cylinders with a representative cylinder indicated
generally by reference numeral 14. In a preferred embodiment, engine 12 is
a multi-cylinder compression-ignition internal combustion engine, such as
a four, six, eight, twelve, sixteen or twenty-four cylinder diesel engine,
for example. Each cylinder 14 includes a piston 16 operatively associated
with a crankshaft 18 via a connecting rod 20 as is well known in the art.
An electronic injector 22 having a solenoid 24 is operatively associated
with a camshaft 26 via rocker arm 28 for controlling fuel delivery to
engine 12. Piston 16 includes piston rings 30 for separating the
combustion chamber 32 from the opposite side of the piston/cylinder 34
which is in fluid communication with crankcase 36 in an open crankcase
ventilation arrangement.
System 10 preferably includes a crankcase pressure sensor which provides a
continuously variable signal indicative of the pressure within crankcase
36. In one embodiment of the present invention, crankcase pressure sensor
38 is a gauge pressure transducer vented to atmosphere with a range of +/-
five volts corresponding to a pressure of +/- one psig. System 10 also
preferably includes an engine speed sensor 39 which senses rotational
speed and/or position of crankshaft 18. System 10 further includes an
accelerator/throttle pedal sensor 40 for determining position of
accelerator pedal 42 which indicates the desired engine torque requested
by the vehicle operator. System 10 may also include various other sensors
44 for generating signals indicative of corresponding operational
conditions or parameters of engine 12 or of the vehicle (not shown).
Sensors 44 may include appropriate sensors for providing signals
indicative of boost pressure, air temperature, oil temperature, oil
pressure, oil level, fuel pressure, vehicle speed, and coolant level, in
addition to appropriate switches connected to an operator interface to
select various optional engine operating modes including a stop engine
override, selection and setting of cruise control, and the like. Engine
and/or vehicle operating parameters or conditions may also be calculated,
determined, or inferred based on one or more of the sensed parameters or
operating conditions indicated by sensors 44. For example, requested
torque may be inferred or determined based on a signal from accelerator
pedal sensor 40. Likewise, engine power may be determined based on engine
speed and requested torque. Various other engine operating parameters or
reference values may be determined in a similar fashion as will be
appreciated by one of ordinary skill in the art.
Sensors 44 are in electrical communication with a controller 46 via input
ports and/or conditioning circuitry 48. In a preferred embodiment,
controller 46 is the DDEC controller available from Detroit Diesel
Corporation, Detroit, Mich. Various other features of this controller are
described in detail in U.S. Pat. Nos. 5,477,827 and 5,445,128, the
disclosures of which are hereby incorporated by reference in their
entirety. Controller 46 preferably includes a microprocessor 50 in
communication with various computer readable storage media 52 via data and
control bus 54. Computer readable storage media 52 may include any of a
number of known devices which function as a read-only memory (ROM) 56,
random access memory (RAM) 58, keep-alive memory (KAM) 60, and the like.
The computer readable storage media may be implemented by any of a number
of known physical devices capable of storing data representing
instructions executable via a computer such as controller 46. Known
devices may include, but are not limited to, PROM, EPROM, EEPROM, flash
memory, and the like in addition to magnetic, optical, and combination
media capable of temporary or permanent data storage.
Computer readable storage media 52 include data representing program
instructions (software), calibrations, operating variables, and the like
used in conjunction with associated hardware to effect control of various
systems and subsystems of the vehicle, such as engine 12. Controller 46
receives signals from sensors 44 via input ports 48 and generates output
signals which may be provided to various actuators 62 and/or components
via output ports 64. Signals may also be provided to a display device 66
which may include various indicators such as lights 68 to communicate
information relative to system operation to the operator of the vehicle.
Of course, alphanumeric, audio, video, or other displays or indicators may
be utilized if desired.
With continuing reference to FIG. 1, control logic implemented by
controller 46 and associated hardware and/or software determines whether
the current crankcase pressure as indicated by pressure sensor 38 has
exceeded a limit associated with current engine operating conditions
according to the present invention. An engine operating value, reference
value, or index value is determined from one or more sensed and/or
calculated engine operating parameters including but not limited to engine
speed (RPM) and desired engine torque. As will be appreciated by one of
ordinary skill in the art, control logic according to the present
invention is preferably implemented by a programmed microprocessor
operating as described in detail below. However, various alternative
hardware and/or software may be used to implement the control logic
without departing from the spirit or scope of the present invention.
A data, diagnostics, and programming interface 70 may be selectively
connected to controller 46 via a connector 72 to exchange various
information between controller 46 and the operator and/or service
personnel. Interface 70 may be used to change values within the computer
readable storage media 52, such as configuration settings, calibration
variables, look-up table values, control logic, pressure thresholds for
detecting engine malfunctions, and the like.
In operation, open crankcase ventilation systems such as illustrated in
FIG. 1 have a crankcase pressure which varies as a function of engine
power. During normal operation, pressure within crankcase 36 will be much
lower than pressure within combustion chamber 32. Various
cylinder/piston-related faults or malfunctions result in an increased
pressure within crankcase 36. While certain mechanical failures will
result in a near total loss of compression within combustion chamber 32
and an associated dramatic increase in crankcase pressure, most faults or
malfunctions occur more gradually. As such, the present invention provides
a system and method for discriminating between increases in crankcase
pressure due to normal operational variations and those indicative of an
impending or gradual failure condition using a crankcase pressure limit
which varies as a function of current engine operating conditions and may
be adjusted or tuned to accommodate various applications.
In a preferred embodiment of the present invention, a crankcase pressure
malfunction or fault is indicated when the measured crankcase pressure
exceeds a corresponding limit value based on current engine operating
conditions. Preferably, the limit value is stored in a computer readable
storage media within a look-up table indexed by at least one measured
and/or calculated engine operating parameter, such as engine speed, engine
load (indicated by requested torque, for example), engine power, or the
like. Sensitivity to determination of a fault condition may be calibrated
or adjusted by a corresponding calibration variable or variables such that
sensitivity is increased at higher engine speeds, loads, or approximately
equal across all speeds and loads. Accordingly, the increased sensitivity
of the present invention provides a system and method for detecting
malfunctions over a range of engine loading and engine speeds. Further,
the present invention provides early detection and warning of engine
malfunction before catastrophic engine failure occurs to facilitate
remedial action by the vehicle operator and/or engine controller.
Referring now to FIG. 2, a graph illustrating calibration and operation of
an engine malfunction detection system or method based on crankcase
pressure according to the present invention is shown. The graph of FIG. 2
represents actual engine operating data for a six cylinder diesel engine
under normal operating conditions. The data 100 represented generally by
lines 102, 104, and 106, represent CCP (kiloPascals) as a function of a
calculated engine operating parameter based on engine speed and requested
torque under "normal" operating conditions, i.e. without a crankcase
pressure fault. Data 100 may be used to determine corresponding crankcase
pressure limit values 108 represented generally by line 110. The
appropriate crankcase pressure limit value (CCPL) is used to determine
when a crankcase pressure fault exists for the current engine operating
conditions as reflected by the selected engine operating parameter (EOP).
Crankcase pressure limit 110 may be established theoretically or
empirically using field tests, engine dynamometer tests, warranty data,
and the like. Likewise, selection of an appropriate EOP indicative of a
particular fault or faults may be selected based on similar testing and
may vary based on the particular application and the particular fault.
The crankcase pressure limit values are preferably calibrated sufficiently
above the maximum anticipated crankcase pressure values which will be
observed under normal operating conditions taking into account
engine-to-engine variability. This will increase the confidence in a fault
determination while reducing the probability of a false detection. Once
the appropriate pressure limit or limits are established, one or more
limit values 108 are stored in computer readable storage media 52,
preferably in the form of a look up table. As will be appreciated by one
of ordinary skill in the art, various intermediate values may be
determined by interpolation, extrapolation, or calculation using
parameters, values, or constants stored in computer readable storage media
52.
In one embodiment of the present invention, a sensitivity or tuning
constant, K.sub.1, is used to adjust the sensitivity of the fault
determination. The graph of FIG. 2 represents an engine operating
parameter based on engine speed and requested torque without a sensitivity
adjustment, or equivalently with a K.sub.1 of zero. As such, fault
detection is more sensitive to pressure variations occurring at higher
engine speeds. Curve 102 represents a line or curve of constant engine
speed (1350 RPM) as requested torque is varied from 0% (corresponding to
engine idle) to 100% (corresponding to 100% throttle). Likewise, curves
104 and 106 represent measured crankcase pressure as a function of a
selected engine operating parameter or reference value which is a function
of a constant engine speed (1650 RPM and 1950 RPM, respectively) as torque
varies from 0% to 100%.
In the embodiment of FIG. 2, the engine operating parameter is represented
by:
EOP=(N.sub.e *TQ.sub.e +K.sub.1 *N.sub.e.sup.2)/(K.sub.1 *K.sub.2 +1)
where N.sub.e represents the engine speed in revolutions per minute (RPM),
(TQ) is the requested engine torque as indicated by the throttle pedal
position sensor, K.sub.1 is the sensitivity constant, and K.sub.2 is a
scaling or normalization factor to scale EOP for various engines. In this
example, K.sub.1 is zero and K.sub.2 represents the RPM limit of 2400. As
such, the sensitivity of the crankcase pressure fault detection, i.e. the
change in CCP required to trigger a fault condition, is adjusted to be
more sensitive to faults occurring at higher engine speeds. This can be
seen by the relatively smaller difference between values of the 1950 RPM
curve 106 and corresponding limit values as compared with values of the
1650 RPM curve 104 or 1350 RPM curve 102. According to the present
invention, the detection sensitivity may be adjusted based on the
particular engine configuration and/or application to improve fault
detection capability and reliability.
FIG. 3 illustrates crankcase pressure data 120 as a function of an engine
operating parameter (which is a function of engine speed and requested
torque) with a sensitivity or adjustment factor K.sub.1 selected to
provide increased sensitivity for higher loads or requested torques. In a
preferred embodiment, K.sub.1 is one-byte calibration constant with a
value between 0 (Hex) and FF (Hex) or equivalently 0 and 255 corresponding
to scaled values ranging from 0 to 0.001275 represented by 5*10.sup.-6 per
bit. FIG. 3 represents a value for K.sub.1 of FF (Hex) and 2400 for
K.sub.2 where the EOP is calculated as described above for FIG. 2.
Constant engine speed curves 122, 124, and 126 in addition to crankcase
limit curve 128 (with representative values 130) are shown for comparison
to FIG. 2. Constant engine load (throttle) curves 132, 134 pass through
corresponding points of constant engine speed curves 122, 124, and 126.
Thus, curve 132 represents observed "normal" crankcase pressure values as
a function of an engine operating parameter for a constant requested
torque or throttle pedal position as engine speed varies from idle to 1950
RPM while curve 134 represents pressure values for a relatively lower
constant throttle pedal position as engine speed varies from idle to 1950
RPM. As such, a crankcase pressure fault condition, which is indicated
when observed crankcase pressure exceeds the corresponding limit value for
the current value of the selected engine operating value, is more
sensitive to higher engine loads relative to the sensitivity illustrated
in FIG. 2.
Referring now to FIG. 4, a graph of crankcase pressure as a function of a
selected engine operating parameter is shown with a sensitivity factor
calibrated to provide approximately equal sensitivity across all engine
speeds and loads. Crankcase pressure limit curve 140 is shown in addition
to constant engine speed curves 142, 144, and 146 corresponding to engine
speeds of 1350, 1650, and 1950 RPM, respectively, and wide-open throttle
curve 148. As illustrated curves 142, 144, 146, and 148 having
corresponding values which are approximately equal across the operating
range of the engine such that the difference between a value on any one of
those curves and the corresponding limit value is about the same. As such,
the system will exhibit substantially equal sensitivity to a crankcase
pressure fault across all engine speeds and loads. The data illustrated
were generated with an EOP calculated as described above with reference to
FIGS. 2 and 3 having a value for K.sub.1 of 30 (hex) or equivalently 48,
and having a value for K.sub.2 of 2400.
As illustrated and described with reference to FIGS. 1 through 4, the
present invention provides an adjustable engine operating parameter which
may be referred to as an index value or reference value, to access or
select a corresponding crankcase pressure limit value, preferably stored
in a look-up table. This provides for adjustable sensitivity and
flexibility in calibrating the crankcase pressure limit while minimizing
memory required to store the look-up table. Rather than adjust the
indexing variable (EOP), a two-dimensional or three-dimensional look-up
table could alternatively be utilized, although clearly not as efficient
in terms of memory utilization. Furthermore, a multi-dimensional look-up
table requires significantly more development time to calibrate and
validate as compared to the preferred method of the present invention
which uses a single-dimensional table or array to store the crankcase
pressure limit values.
Referring now to FIG. 5, a flowchart illustrating operation of a system or
method for detecting engine malfunctions based on crankcase pressure
according to the present invention is shown. As will be appreciated by one
of ordinary skill in the art, the flowchart represents control logic which
may be implemented or effected in hardware, software, or a combination of
hardware and software. The various functions are preferably effected by a
programmed microprocessor, such as the DDEC controller, but may include
one or more functions implemented by dedicated electric, electronic, or
integrated circuits. As will also be appreciated, the control logic may be
implemented using any one of a number of known programming and processing
techniques or strategies and is not limited to the order or sequence
illustrated here for convenience only. For example, interrupt or event
driven processing is typically employed in real-time control applications,
such as control of a vehicle engine or transmission. Likewise, parallel
processing, multi-tasking, or multi-threading systems and methods may be
used to accomplish the objects, features, and advantages of the present
invention. The present invention is independent of the particular
programming language, operating system, processor, or circuitry used to
implement the control logic illustrated.
Crankcase pressure (CCP) is measured as represented by block 150. Current
engine operating conditions are determined as represented by block 152.
This may include determination of the current (instantaneous or average)
engine speed as represented by block 154 and/or current requested engine
torque as represented by block 156. A current index value is determined
based on the current engine operating conditions as represented by block
158. The index value may be calculated using sensed and/or calculated
values representing the current engine operating conditions. A crankcase
pressure limit value is then determined based on the index value as
represented by block 160. Stated differently, the index value defines the
domain of the crankcase pressure limit function whose range is determined,
preferably via a look-up table and appropriate interpolation and/or
extrapolation, as represented by block 160. Of course, the limit value
could be calculated based on appropriate constants and operating
variables, depending upon the particular application requirements. The
current crankcase pressure value is compared to the corresponding limit
valve as represented by block 162. The engine is then controlled based on
the result of the comparison as represented by block 164. If the current
value for CCP is less than or equal to the corresponding limit value,
normal operation continues as represented by block 166. If the current
value for CCP exceeds the corresponding limit value as determined in block
164, then engine control may include reducing available engine torque as
represented by block 168, shutting down the engine as represented by block
170, alerting the operator as represented by block 172 and/or logging a
fault condition or code in the engine controller as represented by block
174. This code may then be used by service personnel or fleet operators in
diagnosing and correcting the fault condition.
As will be recognized by one of ordinary skill in the art, the control
logic illustrated in FIG. 5 is generally repeatedly executed or operated
whenever the engine is running. In a programmed microprocessor
implementation, the control logic executed to sample the sensor signals in
determining the current engine operating conditions and crankcase pressure
may be executed in a background or secondary control loop which repeats
about every 100 msec, for example.
As such, the present invention provides a system and method for detecting a
cylinder/piston fault based on sensed crankcase pressure. The present
invention provides an adjustable sensitivity to facilitate early detection
of various fault conditions while reducing susceptibility to false
indications. System memory is efficiently utilized by adjusting the index
variable based on a desired sensitivity, preferably utilizing a second
order function of engine requested torque and engine speed. The present
invention provides detection sensitivity which can be adjusted to detect
fault conditions more quickly at higher engine speeds, higher engine
loads, or substantially equally across all engine speeds and loads.
While embodiments of the invention have been illustrated and described, it
is not intended that these embodiments illustrate and describe all
possible forms of the invention. Rather, the words used in the
specification are words of description rather than limitation, and that
various changes may be made without departing from the spirit and scope of
the invention.
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